Shielded metal enclosed lightning arrester

ABSTRACT

A high voltage lightning arrester enclosed in a grounded metal enclosure containing a pressurized insulating gas. The arrester is provided with an asymmetrical shield and grading means to control the voltage distribution across the arrester.

United States Patent 1 Osmundsen et al.

SHIELDED METAL ENCLOSED LIGHTNING ARRESTER Inventors: Norman K.Osmundsen; John E.

Harder, both of Bloomington, lnd.; Tohei Nitta, Amagasaki, JapanAssignee: Westinghouse Electric Corporation,

Pittsburgh, Pa. Filed: Oct. 11, 1972 App]. No.: 296,720

US. Cl 317/62, 315/36, 317/70 Int. Cl. H02h 9/06 Field of Search 317/61,62, 70; 315/36 Oct. 23, 1973 [56] References Cited UNITED STATES PATENTS3,099,770 7/l963 Sorrow et al. 317/62 X 3,624,450 11/1971 Graybill3,649,875 3/1972 Nagai et al 3l7/70 X Primary Examiner-James D. TrammellAttorney-A. T. Stratton et a1.

[57] ABSTRACT A high voltage lightning arrester enclosed in a groundedmetal enclosure containing a pressurized insulating gas. The arrester isprovided with an asymmetrical shield and grading means to control thevoltage distribution across the arrester.

10 Claims, 6 Drawing Figures Pmmmumzs ms 3. 767,973

sum 2 [1F 3 PATENIEDO0I23 ma 3. 76719 73 SHEET 3 [IF 3 SHIELDED METALENCLOSED LIGHTNING ARRESTER BACKGROUND OF THE INVENTION The presentinvention relates to high voltage lightning arresters enclosed in agrounded metal enclosure and insulated by a pressurized gas, and moreparticularly to means for controlling the voltage distribution acrosssuch an arrester.

More generally, the invention relates to high voltage, metal enclosed,gas insulated electrical systems. In such systems, the conductors orbusses are enclosed in tubular metal enclosures filled with apressurized gas of suitable properties such as sulphur hexafluoride.Associated devices such as circuit breakers, isolators, groundingswitches and the like are also contained in metal enclosures so that acomplete substation, or this electrical system, can be made up ofcomponents contained in communicating metal enclosures and insulated bythe pressurized gas. Such a system permits a substantial reduction inthe space required, as well as increased reliability and safety andreduced maintenance, with the further advantage that it lends itselfwell to a modular design approach with resulting low installation costs.

The pressurized gas insulation used in these systems permits relativelyclose clearances between the grounded metal enclosure and the highvoltage equipment contained within the enclosure. When a high voltage,such as the line to ground system voltage, is applied across a device insuch close proximity to a grounded surface, however, the electric fieldis badly distorted and the performance of devices such as lightningarresters is adversely affected by the resulting nonuniformity ofvoltage distribution. Other devices such as coupling capacitors, forexample, may also be adversely affected by non-uniform voltagedistribution resulting from the relatively small clearance to adjacentgrounded metal surfaces. Lightning arresters have been used in metalenclosures at relatively low voltages as in Harder U.S. Pat. No.3,469,146, and have been proposed for high voltage, gas insulatedsystems as in Graybill U.S. Pat. No. 3,624,450, but no means forcontrolling the voltage, distribution in such an arrangement has beenavailable, except the conventional grading rings. Such grading rings areapplied to the line terminal, and for high voltage arresters they can beof very large size and high cost and do not necessarily result in thedesired voltage distribution. Furthermore, they are not desirable for ametal enclosed system because of the large amount of space which theyrequire.

SUMMARY OF THE INVENTION The present invention provides a means forcontrolling the voltage distribution across a lightning arresterenclosed in a grounded metal enclosure so as to obtain substantiallyuniform voltage distribution.

In a copending U.S. Pat. application of T. Nitta, Ser. No. 296,716,filed Oct. 11, 1972 and assigned to the assignee of the presentinvention, there is disclosed an asymmetrical shielding means forcontrolling the voltage distribution on high voltage equipment used inmetal enclosed, gas insulated systems. The present invention provides aconstruction for a shield of this general type utilizing elongatedmembers of varying length extending axially on one side of the arresterin combination with an arcuate shield member encircling the top or lineterminal end of the arrester, to control the capacitances to groundalong the length of the arrester. Grading means, such as a series ofrings spaced apart along the length of the arrester, is used to maintaina symmetrical field within the arrester itself and together with theasymmetrical shield formed by the elongated members provides veryeffective means for controlling the voltage distribution to obtainsubstantial uniformity of voltage distribution. An arrester of standarddesign and construction can thus be utilized and its performance will beessentially the same as in the more usual outdoor environment.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fullyunderstood from the following detailed description, taken in connectionwith the accompanying drawings, in which:

FIG. 1 is a front view in elevation and partially broken away showing ashielded arrester enclosed in a metal enclosure;

FIG. 2 is a side view of the arrester and shield;

FIG. 3 is a top plan view of the arrester;

FIG. 4 is a transverse sectional view substantially on the line IV IV ofFIG. '2;

FIG. 5 is a transverse sectional view substantially on the line V-V ofFIG. 2; and

FIG. 6 is a fragmentary elevation view of the line terminal and upperend of the arrester, partially in section on the line VI-Vl of FIG. 3.

DESCRIPTION OF A PREFERRED EMBODIMENT There is shown in the drawings ashielded, high voltage, metal enclosed lightning arrester embodying theprinciples of the invention. As there shown, a lightning arrester 10 isdisposed within a metal enclosure 11 which would normally be groundedand which is generally cylindrical to enclose the arrester 10 with aclearance between the enclosure and the arrester. The enclosurev l l isfilled with a suitable insulating gas such as sulphur hexafluoride at apressure of 45 psig, although other suitable gases or pressures might beused. The pressurized gas insulation makes possible a relatively smallclearance between the enclosure and the arrester and thus reduces thespace required for the installation. It will be understood that themetal enclosed, gas insulated systems to which the invention relates areprimarily intended for use in substations on high voltage transmissionsystems. Thus, these gas insulated systems have been designed forvoltages in the range of 69 KV to 345 KV, for example, although they mayobviously be used for other voltages. At these high voltages, the savingin space due to the reduced clearances is very significant. Therelatively small clearances to ground, however, result in the problem ofnon-uniform voltage distribution mentioned above which would adverselyaffect the performance of lightning arresters and certain other devices,such as coupling capacitors.

The arrester 10 has not been illustrated in detail as it may be anystandard or conventional type of high voltage lightning arresterconsisting of a suitable assembly of spark gaps and valve blocks. Asuitable construc tion and arrangement is shown, for example, in thepatents to Kennon U.S. Pat. No. 3,534,221 and Osterhaut et al. U.S. Pat.No. 3,611,044 although any suitable construction might be utilized. Thearrester 10 is contained in a generally cylindrical housing 12 ofporcelain or other suitable insulating material and which may have asmooth exterior surface. The arrester is closed by a metal end cap 13 atthe upper end which serves for connection to a line terminal and by ametal end cap 14 at the bottom for connection to ground. A lineconductor 15 which may be a rod-like member, either solid or tubular, isconnected to the end cap 13 as more fully described hereinafter forconnection to the equipment to be protected by the arrester, and theconductor 15 is contained in a tubular metal enclosure 16 whichcommunicates with the enclosure 11 and forms part of a complete metalenclosed substation or other electrical system.

In the conventional use of a lightning arrester such as the arrester 10,it is supported on a substation structure or platform support, or othergrounded supporting structure of some type, usually in the open air. Thevoltage distribution across the arrester is then substantially uniform,or can be made sufficiently uniform by conventional grading rings, andthe performance of the arrester is determined on that basis. In theusual outdoor installation, the voltage distribution may be affected bystray capacitances to ground but most of the arrester is sufficientlyremote from the grounded supporting structure that these capacitancesare relatively small and do not seriously affect the voltagedistribution. When the arrester is enclosed in a metal enclosure 11 asin FIG. 1, however, the presence of a grounded conducting surface inclose proximity to the arrester over its entire length has a seriouseffect on the voltage distribution if no means are provided to controlthe electric field. The clearance between the enclosure 11 and thearrester is necessarily relatively small in order to obtain theadvantages of the metal enclosed system discussed. above, and thecapacitances to ground between the arrester and the enclosure 11 aretherefore correspondingly large so that the electric field is seriouslydistorted. The performance of a standard arrester would be adverselyaffected by the resulting non-uniformity of voltage distribution.

In accordance with the present invention, there is provided anasymmetrical shield of the general type disclosed in the above mentionedNitta application to control the voltage distribution across thearrester and thus permit the satisfactory use of a high voltage arresterof standard design.

As shown in FIGS. 1 and 2, the shield is supported on a plate 17 whichmay be made of steel or other conducting material. The plate 17 issupported on the top end cap 13 of the arrester 10 by means of aplurality of bolts 18 which extend through the plate 17 and support itin vertically spaced relation from the end cap 13. It will be noted, asseen in FIGS. 2 and 3, that the plate 17 is circular and is eccentricwith respect to the verti cal axis of the arrester l0, and has anopening 19 therethrough which is substantially concentric with thevertical axis. As shown more clearly in FIG. 6, the terminal means ofthe arrester extend through this opening 19 -in the plate 17. Anysuitable terminal means may be provided for connecting the lineconductor to the arrester. As shown in detail in FIG. 6, the particularconstruction utilized in the present arrester includes an internallythreaded boss 20 on the end cap 13 and preferably integral therewith. Aconnecting sleeve 21 is threaded into the boss 20 and a generallycylindrical contact member 22 is threaded on the sleeve 21. The contactmember 22 may be a, cylindrical steel member internally threaded at oneend to engage the sleeve 21. At the other end, a plurality of contactfingers 23 are pivotally mounted on the contact member 22 and are urgedradially inward by means of springs 24, the contact fingers 23 beingmovable to the necessary extent in radial slots in the member 22. Theconductor 15 engages the spring loaded fingers 23 to effect connectionto the arrester, thus providing a simple, easily engaged connectingmeans.

The asymmetrical shield itself, which is mounted on the plate 17,includes a plurality of elongated conductive members 25. The members 25are elongated metal tubes, preferably closed at the ends as illustrated,and any necessary or desirable number may be utilized. In the embodimentshown in the drawings, five of the elongated members 25 are utilizedarranged in an are around part of the circumference of the plate 17. Themembers 25 are of varying length, the central one being the longest, andextending over most of the axial length of the arrester 10. The otherelongated members 25 progressively decrease in length from the centralmember to the outer members as clearly shown in FIG. 1. The members 25may be mechanically secured and electrically connected to the plate 17by any suitable means such as the brackets 26 which may be welded to themembers 25 and to the plate 17 to rigidly secure the members 25 to theplate. Further rigidity and support for the members 25 may be providedby short rod members 27 welded or brazedin position between the members25 as shown in FIGS. 3 and 4. The asymmetrical shield is completed by anarcuate shield member 28 extending around the end cap 13 into contactwith the members 25 and attached to the plate 17 in any suitable manneras by internal brackets 29. The arcuately arranged tubular members 25extend almost half way around the circumference of the plate 17 and thearcuate shield 28 extends around the remaining circumferential extent ofthe plate 17, so that the elongated members 25 and the shield 28together form a complete circle encircling the upper or line terminalend of the arrester. The elongated members 25 extend axially of thearrester on one side only thereof and thus form an asymmetrical shieldof varying and progressively decreasing circumferential extent. As more'fully explained in the above mentioned Nitta application, the voltageto ground at any point along the arrester 10 is determined by thecapacitance to ground (the enclosure 11) at that point and thecapacitance between the shield and the arresten at the same point. Thus,by proper location and design of the shield the relation of thecapacitances to ground and to the shield can be'determined in a desiredmanner to control the voltage along the length of the arrester and asubstantially uniform distribution of voltage can be obtained.

In order to obtain proper performance of the arrester, the field withinthe arrester itself must be substantially symmetrical about the centerline or axis of the arrester. For this purpose, grading means areprovided within the asymmetrical shield. As shown, the

grading means consists of a series of conducting rings 30 disposed overthe housing 12 of the arrester 10. The rings 30 are conducting rings ofsteel or other suitable material and are arranged in a series uniformlyspaced apart from one end of the arrester to the other as clearly shownin FIGS. 1 and 2. The rings may be supported in position in any suitablemanner. As illustrated, they are supported by three vertical supportbars 31 extending vertically for the full length of the arrester. Thebars 31 may be made of any suitable rigid insulating material and havenotches positioned to engage the rings 31 and support them in position.The bars 31 are secured in position at the top of the arrester by ametal clamp 32 which engages the bars and is secured to a semi-circularclamp 33 on the opposite side of the arrester in a manner to rigidlyclamp the upper ends of the bars 31 in place. At the bottom of thearrester, the bars are similarly engaged by a clamp 34 which is securedto a corresponding clamp 35 located in position by spacing blocks 36.The various clamps are held in place by bolts 37 which rigidly clamp thesupporting bars 31 in place to hold the grading rings 30 in theirdesired positions uniformly spaced from one end of the arrester to theother. It will be seen that the rings 30 float in potential between lineand ground and provide a grading means to maintain a symmetrical fieldwithin the arrester itself in order to obtain the desired performance.

As previously indicated, the bottom terminal cap 14 may be utilized as aground terminal. The enclosure 11 is, of course, grounded and thearrester is mounted on the enclosure 11 with the terminal cap 14electrically connected thereto.

The arrester may, as previously indicated, be of any suitable or usualconstruction. Many arresters are provided with pressure releasediaphragms or blow-out plates of various types at the lower end topermit the escape of gases which may be generated within the arrester incase of failure, so as to prevent explosion of the arrester and damageto other. equipment. When an arrester provided with a'pressure releasemeans of this kind is utilized in the present invention, it is desirableto prevent contamination of the pressurized insulating gas in theenclosure by the gases escaping from the arrester and it is alsodesirable to maintain the integrity of the sealed enclosure to preventescape of the insulating gas or loss of pressure in the closed system.The arrester of the present invention is therefore mounted in theenclosure 11 in a manner to accomplish these purposes. As shown in FIG.1, the bottom plate 38 which forms the bottom wall of the enclosure 11has a central opening 39. The arrester 10 is placed on the plate 38 insuch a position that its axis is concentric with the opening 39 so thatin case of failure of the arrester and release of gas from the interiorof the arrester, it can escape through the opening 39. A sealing gasket40 is placed between the end cap 14 of the arrester and the plate 38with a central opening coextensive with the opening 39. The arrester 10may be held in place by suitable mounting voltages or other means whichwill effect electrical connection to the plate 38. It will be seen thatthe gasket 40 effectively seals the arrester to the bottom plate 38 ofthe enclosure so that if the arrester should fail in service and thepressure release device should operate to permit the escape of gasesgenerated in the arrester, the gases can escape through the opening 39without contaminating the pressurized insulating gas in the enclosure 11and without causing any loss of prsssure or escape of gas from thesealed enclosure. It will be understood that any suitable sealing andmounting means may be utilized to mount the arrester 10 on the bottomplate 38.

It should now be apparent that the shielded lightning arresterconstruction has been provided which makes it possible to obtain uniformvoltage distribution across a high voltage lightning arrester enclosedin a grounded metal enclosure. This makes it possible to use arrestersof standard or conventional design in a metal enclosed, gas insulatedsystem with the same performance as in the more usual outdoorenvironment despite the presence ofa grounded surface in close proximityto the arrester through its entire length. This result is obtained bymeans of the asymmetrical shield in combination with the grading ringsor other means for ensuring symmetry of the electric field within thearrester itself. The particular construction disclosed is a particularlydesirable arrangement for facilitating the design and manufacture ofshields of this type, although it will be apparent that other specificdetails of construction might be utilized.

The invention has been described with particular reference to alightning arrester but it will be apparent that other devices, such ascoupling capacitors for example, may also be adversely affected bynon-uniform voltage distribution and the asymmetrical shield describedabove may also be used with such devices to make it possible to obtainthe desired performance from devices of standard construction.

We claim as our invention:

1. ln combination, a grounded metal enclosure containing an insulatinggas, a lightning arrester disposed within said enclosure, said arresterhaving line terminal means at one end thereof and ground terminal meansat the other end, shielding means in conductive relation with the lineterminal means, said shielding means extending toward said other end ofthe arrester on one side only of the arrester and being of varyinglength axially of the arrester, and grading means encircling thearrester for controlling the electric field within the arrester.

2. The combination of claim 1 in which said grading means comprises aseries of conductive rings spaced apart and extending for substantiallythe entire length of the arrester.

3. The combination of claim 2 in which said shielding means includes aplurality of conducting members of differing lengths.

4. The combination of claim 2 in which said shielding means includes anarcuate member extending around one side of the arrester adjacent theline terminal means and a plurality of elongated members disposed sideby side on the other side of the arrester and forming a complete circlewith said arcuate member, said elongated members extending axially ofthe arrester toward the other end thereof, the central one of theelongated members being of greatest length and the successive members oneach side of the central member being progressively shorter.

5. The combination of claim 4 in which said elongated members are metaltubes closed at both ends.

6. The combination of claim 1 in which said ground terminal meansincludes a conducting bottom cap having a central opening therein, andmeans for attaching said cap to the metal enclosure with a sealedconnection, the enclosure having an opening adjacent said opening in thecap and within the sealed connection.

7. A lightning arrester adapted for use in a gas-filled, grounded metalenclosure, said arrester comprising a housing having line terminal meansat one end thereof and ground terminal means at the other end thereof,asymmetrical shielding means extending axially of the arrester on oneside only, grading means encircling the arrester within the shieldingmeans, said terminal means including a conducting member for supportingbeing of different lengths.

9. A lightning arrester as defined in claim 7 in which said gradingmeans comprises a plurality of conducting rings and means for supportingsaid rings in spaced relation from one end of the arrester to the other.

10. A lightning arrester as defined in claim 9 in which said shieldingmeans includes a plurality of elongated members of varying lengthmounted on said conducting member at one side only of the arrester.

1. In combination, a grounded metal enclosure containing an insulatinggas, a lightning arrester disposed within said enclosure, said arresterhaving line terminal means at one end thereof and ground terminal meansat the other end, shielding means in conductive relation with the lineterminal means, said shielding means extending toward said other end ofthe arrester on one side Only of the arrester and being of varyinglength axially of the arrester, and grading means encircling thearrester for controlling the electric field within the arrester.
 2. Thecombination of claim 1 in which said grading means comprises a series ofconductive rings spaced apart and extending for substantially the entirelength of the arrester.
 3. The combination of claim 2 in which saidshielding means includes a plurality of conducting members of differinglengths.
 4. The combination of claim 2 in which said shielding meansincludes an arcuate member extending around one side of the arresteradjacent the line terminal means and a plurality of elongated membersdisposed side by side on the other side of the arrester and forming acomplete circle with said arcuate member, said elongated membersextending axially of the arrester toward the other end thereof, thecentral one of the elongated members being of greatest length and thesuccessive members on each side of the central member beingprogressively shorter.
 5. The combination of claim 4 in which saidelongated members are metal tubes closed at both ends.
 6. Thecombination of claim 1 in which said ground terminal means includes aconducting bottom cap having a central opening therein, and means forattaching said cap to the metal enclosure with a sealed connection, theenclosure having an opening adjacent said opening in the cap and withinthe sealed connection.
 7. A lightning arrester adapted for use in agas-filled, grounded metal enclosure, said arrester comprising a housinghaving line terminal means at one end thereof and ground terminal meansat the other end thereof, asymmetrical shielding means extending axiallyof the arrester on one side only, grading means encircling the arresterwithin the shielding means, said terminal means including a conductingmember for supporting said shielding means, said conducting memberhaving contact means thereon for engaging a rigid, rod-like conductor.8. A lightning arrester as defined in claim 7 in which said shieldingmeans includes an arcuate member mounted on said conducting member atone side of the arrester and a plurality of elongated members mountedside by side on the conducting member at the other side of the arrester,said elongated members forming a complete circle with the arcuatemember, and the elongated members extending axially of the arrester andbeing of different lengths.
 9. A lightning arrester as defined in claim7 in which said grading means comprises a plurality of conducting ringsand means for supporting said rings in spaced relation from one end ofthe arrester to the other.
 10. A lightning arrester as defined in claim9 in which said shielding means includes a plurality of elongatedmembers of varying length mounted on said conducting member at one sideonly of the arrester.